Cellular communication receivers are subject to a range of interference. At cell borders, the main downlink (DL) interference is generated by neighboring cells. For LTE systems, the decoding performance for the control channel (QPSK coded) determines the limit at which a useful signaling connection can be maintained. It is therefore highly beneficial to improve the decoding performance of QPSK signals in the presence of one or several strong OFDM interferers.
There are several known techniques for attenuating neighbor cell interference. For example, some approaches use statistical properties of the residual noise, estimating its time, spectral and/or spatial characteristics, to determine the decoding parameters for the own cell signals. Items of user equipment (UEs) may be equipped with more than one receive (RX) antennas and can use multi-antenna reception to produce covariance estimates of noise and interference for use in interference suppression. Such methods can be viewed as a way of combining the RX antennas so that a suitable antenna beam pattern is formed for suppressing the direction of the strongest interferer. Such methods have the attraction of not requiring decoding of the interferer. However, relatively better performance can be achieved with more sophisticated schemes.
For example, higher performance may be obtained through use of one or more interference cancellation methods where the interfering signal is determined and subtracted from the received signal. Joint Detection (JD) processing represents one such approach. With JD processing, the symbols transmitted from the serving transmitter and the interfering transmitter are jointly determined. However, JD processing increases complexity because it relies on having significantly more “system” information available at the receiver. Such information generally must be available for all (cell) signals being jointly detected, such as channel estimates, modulation formats, pilot patterns, transmit diversity modes, etc. Furthermore, JD processing of one interfering signal, along with the desired signal, effectively doubles the channel estimation overhead and can easily more than double the overall decoding processing.
At the expense of further processing, JD processing can be combined with successive interference cancellation, often referred to as “SIC.” A SIC receiver decodes the IQ symbols from an interfering signal and uses them to correct errors in the JD soft values. The true interferer is then re-generated and its impact on the received (RX) symbols is subtracted. This processing yields typically high performance, but obviously is even more costly than JD alone.